Scalable seeding for Sequelize with Node.js?

Question

I want to set up a piece of code that resets my whole database and seeds everything.

The problem is that with a few Foreign Key constraints, the seeds need to happen in order, however those seeds that are not dependent should happen at the same time asynchronously.

How can I define these seeds in separate files properly?

Answer 1

The problem comes down to exporting Promises with module.exports.

When I was requiring a file that returned a Promise directly, the Promise was immediately called.
I solved the problem by returning functions that return the Promise.

Resetting DB and seeding

const Seed = require('../seeds/index');

sequelize.sync({ force: true }).then(() => {
    return Seed();
}).then(() => {
    // DB reset
}).catch(err => {
    // Error in one of the seeds, specific error in 'err'
});

seeds/index.js - Calling the seeds in other files

const UserSeed = require('./user');
const BComponentSeed = require('./bcomponent');
const MaterialSeed = require('./material');

module.exports = function() {
    return Promise.all([ // Returning and thus passing a Promise here
        // Independent seeds first
        UserSeed(),
        BComponentSeed(),
        MaterialSeed(),
    ]).then(() => {
        // More seeds that require IDs from the seeds above
    }).then(() => {
        console.log('********** Successfully seeded db **********');
    });
}

seeds/user.js - Example of the User seed

const User = require('../models/user');
const crypto = require('../globs/crypto');

module.exports = function() {
    return User.bulkCreate([ // Returning and thus passing a Promise here
        {
            email: '[email protected]',
            password: crypto.generateHash('john'),
        },
        {
            email: '[email protected]',
            password: crypto.generateHash('a'),
        },
    ]);
};

Came up with this while responding to this GitHub issue